recipients

The Recipients submodule exposes flat, list-agnostic CRUD over `campaign_recipient` rows through CampaignRecipientService — a lighter-weight counterpart to the recipient-management endpoints nested under Recipient Lists. Where the recipient-lists submodule manages recipients in the context of a specific list (bulk import, CRM sync, public signup, list counter recalculation), this submodule is for direct, single-record access: looking up, editing, or removing one recipient by its own ID regardless of which list it belongs to.

Creating a recipient here still requires a `list_id` and upserts by email within that list, mirroring the same uniqueness rule enforced elsewhere (one recipient row per email per list). Updates allow changing the status — including the terminal/blocking statuses `unsubscribed`, `suppressed`, `bounced`, and `invalid` that CampaignDispatchService and CampaignEmailWorkerService check before including a recipient in a send. Email values are normalized to lowercase on both create and update so that lookups and deduplication remain case-insensitive throughout the module.

Unlike the recipient-lists submodule's recipient endpoints, this submodule does not call `recalculateCounters()` on the owning list after create/update/delete — callers that need the list's rolled-up counts to reflect a change made through this submodule should expect a slight staleness until the next list-level recipient mutation triggers a recalculation.